The present disclosure relates to a content addressable memory and is particularly applicable to the content addressable memory which is able to be built in a semiconductor device and the semiconductor device in which the content addressable memory is built.
A storage device which is called an associative memory or a CAM (Content Addressable Memory) is adapted to search for a data word which matches a search word (search data) from among data words (entries) that the storage device stores therein and to output an address of the data word in a case where the data word which matches the search word is found.
There are a BCAM (Binary CAM) and a TCAM (Ternary CAM) in the CAM. Each memory cell of the BCAM stores information of either “0” or “1”. On the other hand, each memory cell of the TCAM is able to store information of “don't care” in addition to the information of “0” and “1”. “don't care” indicates that either “0” or “1” will do. A searching operation of the TCAM is large in power consumption and power reduction is an object to be resolved in the TCAM.
Japanese Unexamined Patent Application Publication No. 2001-167585 discloses a technology which “controls, in a case where a content of a Valid bit which indicates whether a content of an entry in an associative memory is valid or invalid is valid in a searching operation, so as to pre-charge a match line ML of the entry and controls, in a case where the Valid bit is invalid, so as not to pre-charge the match line ML of the entry”.